Api updates for wearable extensions to notifications

1. Move Extender outside of Builder
2. Rename apply/applyTo to extend
3. Move Wearable extenders into Notification.java
4. Collapse Builder model into single classes
5. Use Bundle for storage: no new parcelable types.

Minor fix to RemoteInput to use flags int for boolean options.

Change-Id: I40012fd0458ec103eabf75ed4c91f636e02f4c8f